In fact, some properties do not have letterboxes and some have letterboxes in unusual places. Also, sometimes we cannot get into flats too.
If the deliverer is unfamiliar with the area he or she is delivering to it is very unlikely they will find all the relevant properties and all the letterboxes.
We aim to deliver to every letterbox in the drop area, however it is not usually possible to achieve 100% penetration with unaddressed material.
At DOR-2-DOR, we generally achieve better than 95% coverage, therefore on a run of 10,000 households (a typical drop) 500 households may not get one.
There is no unaddressed leaflet distribution service (including the Royal Mail that guarantees 100% coverage.